Investigating the design challenges of EV charging

The pandemic saw a pivot point for electric vehicle sales. Sales of all consumer vehicles plunged to levels not seen in Europe since the early 1940s. As we emerged from lockdowns across the region, the shift in consumer preferences for buying an electric vehicle became very apparent. The reasons behind this shift come from several factors, including environmental concerns, a fundamental move to hybrid working, and sustainability. In its recent EY Mobility Lens Consumer Index, EY, a management consultancy, highlighted that 41 % of consumers globally intended to purchase an electric or hybrid vehicle - see Figure 1.

Figure 1 - Global powertrain preferences of consumers planning to buy a car (Source: EY Mobility Consumer Index)

Electrical and electronic design challenges of EV charging stations

As EV sales continue to grow, vehicle manufacturers continue to adapt vehicle platforms to incorporate hybrid and fully electric variants while investing heavily in developing new models. Leading manufacturers that were first to market with an EV line-up are now introducing the second generation of their portfolio. These new models take full advantage of technological advancements in battery research, in-vehicle networking and weight reduction strategies.

One well-known consumer factor against buying an electric vehicle is range anxiety, the fear of running out of charge. This concern appears to be subsiding as next-generation vehicle platforms deliver improved range capabilities and governments push ahead with EV charging infrastructure initiatives. All EVs include an onboard AC charger, typically a 7 kW unit, for overnight charging from a single-phase domestic mains supply. Some homes may opt to have a three-phase installed, bringing the ability to deliver up to 20 kW to the vehicle. However, only the dedicated infrastructure of high-power DC chargers can deliver significant range capability in 30 minutes or less.

From an engineering perspective, high-power DC EV chargers represent a complex challenge, requiring high-power electrical, general electronic hardware, embedded systems, wireless communication, and mechanical disciplines.
 

EV charging stations

When it comes to EV charging, the higher the charging power delivery capability, the quicker a vehicle's battery pack will charge. Not all first-generation cars can accommodate the extremely high charging rates of the fast "super" chargers, but most newer EV platforms can. The industry's informal goal is to bring charging times to that of filling the tank of a petrol or diesel vehicle, which usually is about five minutes or less. That possibility has almost become a reality. Figure 2 illustrates the capacity and typical charging times for various DC charger types. The DC fast charging posts and associated electrical infrastructure is becoming a familiar sight in car parks, supermarkets, business parks, and highway service stations.

Figure 2 - High power capacity DC electric vehicle charging posts offer significant improvements in charging times 

Domestic electrical installations are not typically sufficient to power a fast charger unit, requiring a commercial three-phase supply. Providing a three-phase supply to the home would depend on the local electrical distribution network and, even if possible, would be expensive to install.

EV charger architecture

Figure 3 illustrates the high-level architecture of a DC charger. High-power AC/DC converters take a three-phase supply to provide a high voltage DC supply to the electric vehicle. As highlighted in Figure 2, the level of power capability uses a modular approach. The sheer amount of power involved, up to 1,000 A at 400 VDC, requires heavy-duty electrical engineering, interconnect and cabling components. The mechanical design requires strict attention to thermal management constraints, involving baseplate and forced air cooling for chargers located in warm climates. DC/DC converter efficiencies benefit from technology advancements such as wide-bandgap semiconductors and innovative converter topologies. As conversion efficiencies improve, the amount of waste heat to dissipate reduces, easing thermal management challenges and improving component reliability characteristics.

Figure 3 - The high-level architecture of a DC charger

A current trend in the EV industry is the move from a 400 VDC battery pack to using 800 VDC. As battery chemistry and battery monitoring techniques advance, the 800 VDC approach enables faster charging, reducing charge currents, and permitting the use of lighter-weight cables.

Safety and protection feature highly in fast EV chargers, protecting against excess currents, leakage currents, and high temperatures. EV batteries require constant monitoring during charging and discharging, and the vehicle's battery management system (BMS) provides additional measures to detect potential problems. Communication between the BMS and the charger's control system informs battery condition, charge status, and other parameters it might use to change the charging behaviour.

A touchscreen human-machine interface (HMI) provides EV users access to the charging facilities, user account validation, and secure online wireless access to billing and other customer service functions. Energy usage data is also provided to the AC grid and charger infrastructure operators.

Standards are still evolving across the industry, but key specifications already exist for charging connectors, electrical wiring and safety, charging protocols, and vehicle-to-grid communication. The EV charging infrastructure varies from country to country, with little interoperability between charger infrastructure operators. Currently, EV owners may require accounts with multiple providers, particularly when on long trips away from home. However, operator collaboration will solve this challenge as EV adoption grows and nation-states push for more significant investments in charger infrastructure and compatibility.
 

Don't forget to include interconnect!

Wired connection reliability is an essential aspect of an EV charger's design. This criterion applies to the charger-to-vehicle DC cables, and all internal board-level interconnects. Given the exposed operating environment of an EV charger and the fact it is required to provide an essential service 24/7, continued operation is paramount. Each cable termination, inputs from small signal sensors, flexible PCB connectors for display panels, to DC converter module drive circuitry form a critical link in the operation of an EV charger.

With so many connection points, it’s worth considering a supplier with a range of off-the-shelf components that can meet all of your requirements. Molex’s broad portfolio includes  diverse, reliable solutions for internal board-level connections, whether on the power or control board of an EV charger.

EV charging infrastructure crucial to EV sales growth

According to the European Alternative Fuels Observatory, a transport consultancy, a nine-fold increase in EV charger deployment is required to support the sales growth of electric vehicles - see Figure 5. The average rate of 2,000 chargers installed per week in Europe currently falls short of the 14,000 per week needed to achieve the required numbers by 2030.

Figure 4 - EV charging points current vs required 2021 - 2030 

As with many new technology deployments, building out the charging infrastructure in advance of future revenues is a delicate balance. Most importantly, sales of new electric vehicles continue to grow as consumers opt for a more environmentally-friendly and sustainable approach to their transport needs.

If you’re designing EV charging stations and need access to reliable board-level interconnects, get started by exploring Molex’s range. You can also download this handy Molex reference design to understand exactly which components to use for which connections. Alternatively, if you you’re ready to discuss your requirements with our FAEs, you can get in touch in your local language.

Download the Molex reference design